1. Field of the Invention
The present invention relates generally to hydraulic pump devices and more specifically to a variable displacement hydraulic pumping mechanism that can be operated in both driving and driven configurations and has particular application in mechanical power transmission apparatus.
2. Description of the Prior Art
The hydraulic variable displacement pump device has two principal applications, the transmission of rotary mechanical power and the pumping of fluids. As a transmission, it can accomplish torque multiplication to increase or decrease output torque relative to input torque; speed multiplication to increase or decrease output speed relative to input speed; reversal of direction of rotation (i.e., from clockwise to counterclockwise or vice versa); connection or disconnection of input power from output load as in a conventional clutching mechanism; braking of the output shaft by causing the load to drive the input motor against a drag; and locking of either the input or output shaft so that it cannot rotate. In addition, it can be used as a rotational angular positioning servo to place an output shaft at a prescribed angular position and to hold or maintain the position of a driven body as a function of time as, for example, a gun turret or antenna pointing mechanism. Moreover, it can be used to transfer any of the above functions to a point remote from the power source, and it can be used to drive two or more loads independently.
When used as a pump the variable displacement device can cause a fluid to be transported from one place to another or to have its pressure or velocity of flow increased; supply a prescribed quantity of fluid or rate of flow. Since the pump is of the positive displacement type such that at fixed displacement the quantity of fluid delivered is directly proportional to the number of shaft rotations and the rate of flow is proportional to the rotational speed of the shaft (If the pump is driven by the flow fron another source, it also can function as a flow meter to measure the quantity or rate of flow delivered by the source); supply a variable rate and direction of flow while input speed is fixed (by using variable and reversible displacement); and when operated at constant input torque and variable displacement, it can provide a variable output pressure.
Although clutches, fluid couplings, torque converters, gear trains, and automatic transmissions perform some of the above-mentioned functions, the only devices known which can perform all of the functions listed above are positive, variable displacement hydraulic drives.
Prior art devices of this type are disclosed in the U.S. Pat. Nos. to Sherman, 2,401,376; Pichon, 3,832,198; Van Cleve, 2,962,864; Harris, 3,095,708; Parr, 3,487,787; Briggs, 3,570,246; and Bennetto, 3,730,145. However, such devices suffer substantial disadvantages ranging from mechanical complexity and manufacturing impracticality to extreme operational inefficiency.